Photometric and redshift surveys are a key tool for cosmology.
They allow to follow the evolution of galaxies from high-z to the local universe
to understand their nature:
how they formed, how they evolve.
From the comparison with models of galaxy formation and evolution it
is possible to understand what are the main physical mecanisms at play and the associ ated timescales.

Statistical studies: Evolution of Luminosity and Mass Function and Star/Mass Formation History
Luminosity Function of starburst/AGN in the FIR
Luminosity Function of radio sources and type1 AGN optically-selected